Miller announced
on Twitter that he'd left his previous employer, Accuvant, a
security-research firm, and that he'd be working for Twitter from
St. Louis.

This is a really good move for Twitter.

First of all, Twitter security is a joke right now, as hackers
delight in proving time and again. While Twitter's no doubt doing
sophisticated things on the backend, on the user side, it pretty
much depends on passwords and linked email accounts. As Wired
writer Mat Honan found out recently,
that's not enough.

Second, as Twitter gets more deeply embedded into iOS, Apple's
mobile operating system, it makes sense to have someone who
understands that system's vulnerabilities—so an iPhone
vulnerability doesn't become a backdoor into a user's Twitter
account. (Ultimately, Honan's hacking happened because
of an Apple security flaw—but his Twitter account was compromised
as a result.)